$ cat /etc/crypttab
cryptswap1 /dev/sda4 /dev/urandom swap,cipher=aes-cbc-essiv:sha256
LUKS_boot UUID=160fa39a-1205-4ad5-be44-9c2c943fb113 /usr/local/lib/.keyfile luks,keyscript=/usr/local/sbin/luks_keyfile.sh
LUKS_Hephaestion UUID=4ead8975-c34f-4922-8d0c-25a673ea7d2b /usr/local/lib/.keyfile luks,keyscript=/usr/local/sbin/luks_keyfile.sh
LUKS_Hephaestion_VM UUID=caa161bb-118a-447c-bcab-cbbe412a138a /usr/local/lib/.keyfile luks,keyscript=/usr/local/sbin/luks_keyfile.sh

tj@hephaestion:/home/all/SourceCode/linux/linux$ cat /usr/local/sbin/luks_keyfile.sh
#!/bin/sh
# read a LUKS encryption key-file and write it to STDOUT
if [ ! -n "$1" ]; then
 # report error if no command-line parameter
 exit 1
else
 cat "$1"
 exit 0
fi